Zoom lens

ABSTRACT

A zoom lens is disclosed, having, in order from the object side, a negative first lens unit, a negative or positive second lens unit, a positive or negative third lens unit and a fourth lens unit. The second and third lens units have refractive powers of opposite sign to each other. When zooming from the wide-angle side to the telephoto side, the first to fourth lens units move toward the object side, while simultaneously varying their lens separations.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to zoom lenses and, more particularly, to zoomlenses of compact form, which nevertheless get a high zoom ratio.

2. Description of the Related Art

Recent minimization of the bulk and size of leaf shutter type cameras orthe like has led to a demand for shortening the total length of thecompact zoom lens.

In Japanese Laid-Open Patent Application No. Sho 57-201213, there isproposed a compact zoom lens comprising two lens units of plus-minusrefractive power from the object side with the air separation betweenthese lens units being varied to effect zooming.

Also, the use of three lens units of minus-plus-minus refractive powerin the zoom lens, which are movable for zooming, is proposed in, forexample, Japanese Laid-Open Patent Applications No. Sho 63-271214, No.Sho 64-72114, etc. In these publications, the relation in which thefirst, second and third lens units move during zooming, and theconstruction and arrangement of the constituent parts of the three lensunits are specified to thereby well correct any variation of aberrationswith zooming. Thus, a relatively compact lens system having a highoptical performance at a zoom ratio of 2 to 3 with 8 or 9 lens elementsas a whole is achieved.

An example of adaptation of the zoom lens to the leaf shutter camera byextremely reducing the number of lens elements is proposed in JapaneseLaid-Open Patent Application No. Sho 63-276013.

In this Japanese Laid-Open Patent Application No. Sho 63-276013, thefront lens unit comprises negative and positive, refractive power ortwo, lenses, while the rear lens unit comprises positive and negativerefractive power lenses. Thus, a zoom lens composed of four lenselements in total is achieved. However, because the zoom lens uses arefractive power distribution type lens (GRIN lens), the difficulty inmanufacturing the zoom lens is extremely high, causing the amount oflenses produced through mass production to become low.

Further, Japanese Laid-Open Patent Application No. Sho 64-88512 (U.S.Pat. No. 4,756,609) discloses a zoom lens having four lens units of aminus-plus-plus-minus refractive power arrangement, of which the firstand second lens units each comprise one lens element, the third lensunit is a cemented lens, and the fourth lens unit comprises three lenselements of plus-minus-minus refractive power.

Also, in Japanese Laid-Open Patent Application No. Sho 62-235916, thereis disclosed a zoom lens having four lens units of aminus-plus-plus-minus refractive power arrangement, wherein the firstlens unit is constructed with two elements of plus-minus refractivepower, the second lens unit with three elements of plus-plus-minusrefractive power, the third lens unit with one element, and the fourthlens unit with two elements of minus-plus refractive power.

SUMMARY OF THE INVENTION

An object of the invention is to provide a compact zoom lens of highrange, while still having an optical performance not inferior to that ofthe prior known zoom lenses.

Another object is to achieve a reduction in the total number ofconstituent elements of the zoom lens.

A zoom lens of the present invention is constructed with a first lensunit of negative refractive power, a second lens unit of negative orpositive refractive power, a third lens unit of positive or negativerefractive power and a fourth lens unit of negative refractive powerarranged in this order from the long conjugate side (in the usual term,the object side), the separations between the lens units being varied toperform zooming, wherein the refractive powers of the second and thirdlens units are of opposite sign to each other.

Further, according to embodiments to be described later, for the purposeof zooming from the wide-angle end to the telephoto end, the first,second, third and fourth lens units move toward the long conjugate side.

Further, it is desired that the zoom lens of the invention satisfies thefollowing conditions:

    |D.sub.3w -D.sub.3t |>3|D.sub.2w -D.sub.2t |                                                (1)

    |D.sub.3w -D.sub.3t |>3|D.sub.1t -D.sub.1w |                                                (2)

where D_(iw) is the separation between the i-th and (i+1)st lens unitsin the wide-angle end of the zooming range, and D_(it) is the separationbetween the i-th and (i+1)st lens units in the telephoto end.

Further, as will be seen from the embodiments, the zoom lens of theinvention has its first and second lens units each made up by a singlelens, its third lens units by either a single lens of positive ornegative power, or a cemented lens composed of negative and positivelenses, and its fourth lens unit by a positive single lens and anegative single lens, while still permitting the realization of goodoptical performance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal section view of a numerical example 1 of a zoomlens of the invention.

FIG. 2 is a longitudinal section view of a numerical example 2 of a zoomlens of the invention.

FIG. 3 is a longitudinal section view of a numerical example 3 of a zoomlens of the invention.

FIGS. 4(A), 4(B) and 4(C) are graphic representations of the aberrationsof the numerical example 1.

FIGS. 5(A), 5(B) and 5(C) are graphic representations of the aberrationsof the numerical example 2.

FIGS. 6(A), 6(B) and 6(C) are graphic representations of the aberrationsof the numerical example 3.

FIG. 7 is a longitudinal section view of a numerical example 4 of a zoomlens of the invention.

FIG. 8 is a longitudinal section view of a numerical example 5 of a zoomlens of the invention.

FIG. 9 is a longitudinal section view of a numerical example 6 of a zoomlens of the invention.

FIGS. 10(A), 10(B) and 10(C) are graphic representations of theaberrations of the numerical example 4.

FIGS. 11(A), 11(B) and 11(C) are graphic representations of theaberrations of the numerical example 5.

FIGS. 12(A), 12(B) and 12(C) are graphic representations of theaberrations of the numerical example 6.

FIG. 13 is a longitudinal section view of a numerical example 7 of azoom lens of the invention.

FIG. 14 is a longitudinal section view of a numerical example 8 of azoom lens of the invention.

FIGS. 15(A), 15(B) and 15(C) are graphic representations of theaberrations of the numerical example 7.

FIGS. 16(A), 16(B) and 16(C) are graphic representations of theaberrations of the numerical example 8.

In the longitudinal section views and the aberration curves, referencenumeral 1 denotes the first lens unit, 2 denotes the second lens unit, 3denotes the third lens unit, 4 denotes the fourth lens unit, referencecharacter M stands for the meridional curve, S stands for the sagittalcurve, d stands for the d-line, and g stands for the g-line.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIGS. 1 to 3 and FIGS. 7 to 9, there are depicted the lens forms andthe lens movements represented by the numerical data for numericalexamples 1 to 6 of the invention.

In the drawings, reference numeral 1 denotes a first lens unit arrangedon the object side (long conjugate side), having a negative refractivepower and, here, comprising a negative meniscus lens convex toward theobject side. Reference numeral 2 denotes a second lens unit likewisecomprising a negative meniscus lens convex toward the object side.Reference numeral 3 denotes a third lens unit having a positiverefractive power and comprising either a cemented lens composed of apositive lens having a strong convex surface facing the image side(short conjugate side) and a negative lens, or a bi-convex single lens.Reference numeral 4 denotes a fourth lens unit having a negativerefractive power and comprising a positive lens having a strong convexsurface facing the image side followed, after a spacing therefrom, by anegative lens having a strong concave surface facing the object side.

The first lens unit 1 to the fourth lens unit 4 move toward the objectside when zooming from the wide-angle end to the telephoto end. In thezoom lenses of FIGS. 1 to 3 and FIG. 9, as zooming is effected from thewide-angle end W to the telephoto end T, the separation between thefirst and second lens units increases, the separation between the secondand third lens units decreases, and the separation between the third andfourth lens units decreases. In the zoom lenses of FIGS. 7 and 8, theseparation between the first and second lens units decreases, theseparation between the second and third lens units decreases, and theseparation between the third and fourth lens units decreases.Incidentally, the arrows in the drawings schematically show thedirection of movement and do not trace the loci of motion. Further, ofthe embodiments, there are ones in which the first and third lens unitsmove in unison during zooming.

In addition, the zoom lens of each embodiment of the invention is madeto satisfy the following conditions:

    |D.sub.3w -D.sub.3t |>3|D.sub.2w -D.sub.2t |                                                (1)

    |D.sub.3w -D.sub.3t |>3|D.sub.1t -D.sub.1w |                                                (2)

where D_(iw) is the separation between the i-th and (i+1)st lens unitsin the wide-angle end of the zooming range, and D_(it) is the separationbetween the i-th and (i+1)st lens units in the telephoto end.

The inequalities (1) and (2) are to regulate the varied separationbetween the third and fourth lens units at the wide-angle end and thetelephoto end in relation to the varied separations between the secondand third lens units and between the first and second lens units,respectively. When each condition is violated, not only the variousaberrations become difficult to correct, but also the size of the entirelens system increases objectionably.

Further, it is desirable that the zoom lenses of FIGS. 1 to 3 satisfy atleast one of the following conditions:

    -100<F.sub.1 /F.sub.3 <-10                                 (3)

    -9<F.sub.2 /F.sub.3 <-3                                    (4)

    0.5<F.sub.3 /F.sub.W <1.0                                  (5)

    -1.0<F.sub.4 /F.sub.W <-0.5                                (6)

where Fi is the focal length of the i-th lens unit and F_(W) is theshortest focal length of the entire lens system.

The meanings of the limit values of the inequalities (3) to (6) areexplained below.

The inequality (3) and the inequality (4) are concerned respectivelywith the ratios of the focal lengths of the first and second lens unitsto the focal length of the third lens unit. When the refractive power ofthe first or second lens unit is too weak as exceeding the lower limitof each condition, the longitudinal chromatic aberration becomesdifficult to correct.

When the refractive power of the third lens unit is too weak asexceeding the upper limit, it becomes difficult to secure the back focaldistance in the wide-angle end.

The inequality (5) is concerned with the ratio of the focal length ofthe third lens unit to the shortest focal length of the entire lenssystem. When the refractive power of the third lens unit is too strongas exceeding the lower limit, this lens unit becomes highly sensitive,thus becoming difficult to manufacture. So, it is no good. When therefractive power of the third lens unit is too weak as exceeding theupper limit of the inequalities of condition (5), it becomes difficultto secure the back focal distance in the wide-angle end.

The inequality (6) is concerned with the ratio of the focal length ofthe fourth lens unit to the shortest focal length of the entire lenssystem. When the refractive power of the fourth lens unit is weaker thanthe lower limit, a predetermined zoom ratio becomes difficult to obtain,or it interferes with the third lens unit in the telephoto end. So, itis no good. When the refractive power of the fourth lens unit isstronger than the upper limit, it becomes difficult to correct for avariation of the various aberrations.

The numerical examples are described below. The character r representsthe radius of curvature, d the lens thickness or lens separation, n therefractive index for the d-line and ν the Abbe number.

The aspheric surface is expressed by the following equation for theaxial deviation x in terms of the radius R of the osculating sphere andthe height H from the optical axis:

    x=R(1-(1-H.sup.2 /R.sup.2).sup.1/2)+AH.sup.2 +BH.sup.4 +CH.sup.6 +DH.sup.8 +EH.sup.10 +

    ______________________________________                                        Numerical Example 1 (FIGS. 1, 4(A), 4(B) and 4(C))                            ______________________________________                                        F = 36.19-101.5   FNo = 1:4.1-8.8   2ω = 61.8°-24.0°      r 1 = 50.000                                                                            d 1 = 1.50  n 1 = 1.603111                                                                            ν 1 = 60.7                               r 2 = 45.651                                                                            d 2 = Variable                                                      r 3 = 24.178                                                                            d 3 = 1.50  n 2 = 1.77250                                                                             ν 2 = 49.6                               r 4 = 19.520                                                                            d 4 = Variable                                                      r 5 = 95.414                                                                            d 5 = 5.00  n 3 = 1.49700                                                                             ν 3 = 81.6                               r 6 = 9.695                                                                             d 6 = 1.50  n 4 = 1.83400                                                                             ν 4 = 37.2                               r 7 = -12.299                                                                           d 7 = 1.00                                                          r 8 = Stop                                                                              d 8 = Variable                                                      r 9 = -68.986                                                                           d 9 = 3.50  n 5 = 1.59551                                                                             ν 5 = 39.2                               r 10 = -26.500                                                                          d 10 = 4.64                                                         r 11 = -13.971                                                                          d 11 = 1.70 n 6 = 1.69680                                                                             ν 6 = 55.5                               r 12 = 206.234                                                                ______________________________________                                        Variable   Focal Length                                                       Separation 36.20        63.84  101.50                                         ______________________________________                                        d 2        2.00         1.18   1.93                                           d 4        8.32         8.14   7.38                                           d 8        16.65        7.09   2.51                                           ______________________________________                                                 r 3 is aspherical.                                                            A = 0                                                                         B = -4.43765 × 10.sup.-5                                                C = -2.81409 × 10.sup.-7                                                D = -1.36697 × 10.sup.-9                                                E = -9.28334 × 10.sup.-12                                               r 7 is aspherical.                                                            A = 0                                                                         B = 1.40440 × 10.sup.-5                                                 C = 5.14255 × 10.sup.-8                                                 D = 0, E = 0                                                                  r 10 is aspherical.                                                           A = 0                                                                         B = -3.21458 × 10.sup.-5                                                C = -1.00841 ×  10.sup.-7                                               D = -2.99727 × 10.sup.-10                                               E = -3.58134 × 10.sup.-12                                      ______________________________________                                    

    ______________________________________                                        Numerical Example 2 (FIGS. 2, 5(A), 5(B) and 5(C))                            ______________________________________                                        F = 36.2-101.5   FNo = 1:4.1-8.8   2ω = 61.8°-24.0°       r 1 = 50.000                                                                            d 1 = 1.50  n 1 = 1.71300                                                                             ν 1 = 53.8                               r 2 = 46.140                                                                            d 2 = Variable                                                      r 3 = 22.158                                                                            d 3 = 1.50  n 2 = 1.85026                                                                             ν 2 = 32.3                               r 4 = 18.121                                                                            d 4 = Variable                                                      r 5 = 102.458                                                                           d 5 = 5.00  n 3 = 1.51633                                                                             ν 3 = 64.2                               r 6 = -9.096                                                                            d 6 = 1.50  n 4 = 1.83400                                                                             ν 4 = 37.2                               r 7 = -12.188                                                                           d 7 = 1.00                                                          r 8 = Stop                                                                              d 8 = Variable                                                      r 9 = -57.224                                                                           d 9 = 3.50  n 5 = 1.56732                                                                             ν 5 = 42.8                               r 10 = -25.174                                                                          d 10 = 4.86                                                         r 11 = -13.760                                                                          d 11 = 1.70 n 6 = 1.69680                                                                             ν 6 = 55.5                               r 12 = 620.901                                                                ______________________________________                                        Variable   Focal Length                                                       Separation 36.20        63.84  101.51                                         ______________________________________                                        d 2        1.00         1.11   1.78                                           d 4        8.53         8.42   7.75                                           d 8        16.84        7.24   2.64                                           ______________________________________                                                 r 3 is aspherical.                                                            A = 0                                                                         B = -3.94324 × 10.sup.-5                                                C = -2.31323 × 10.sup.-7                                                D = -1.42198 × 10.sup.-9                                                E = -8.95882 × 10.sup.-12                                               r 7 is aspherical.                                                            A = 0                                                                         B = 1.08432 × 10.sup.-5                                                 C = 3.94859 × 10.sup.-9                                                 D = 0, E = 0                                                                  r 10 is aspherical.                                                           A = 0                                                                         B = -3.23425 × 10.sup.-5                                                C = 2.25379 ×  10.sup.-8                                                D = -1.4729 × 10.sup.-9                                                 E = 3.38991 × 10.sup.-12                                       ______________________________________                                    

    ______________________________________                                        Numerical Example 3 (FIGS. 3, 6(A), 6(B) and 6(C))                            ______________________________________                                        F = 36.19-101.52   FNo = 1:4.1-8.75   2ω = 61.8°-24.0°    r 1 = 50.000                                                                            d 1 = 1.50  n 1 = 1.71300                                                                             ν 1 = 53.8                               r 2 = 46.140                                                                            d 2 = Variable                                                      r 3 = 24.306                                                                            d 3 = 1.50  n 2 = 1.83400                                                                             ν 2 = 37.2                               r 4 = 19.736                                                                            d 4 = Variable                                                      r 5 = 110.499                                                                           d 5 = 5.00  n 3 = 1.51633                                                                             ν 3 = 64.2                               r 6 = -9.591                                                                            d 6 = 1.50  n 4 = 1.85026                                                                             ν 4 = 32.3                               r 7 = -12.403                                                                           d 7 = 1.00                                                          r 8 = Stop                                                                              d 8 = Variable                                                      r 9 = -66.429                                                                           d 9 = 3.50  n 5 = 1.56732                                                                             ν 5 = 42.8                               r 10 = -25.943                                                                          d 10 = 4.69                                                         r 11 = -13.927                                                                          d 11 = 1.70 n 6 = 1.69680                                                                             ν 6 = 55.5                               r 12 = 258.899                                                                ______________________________________                                        Variable   Focal Length                                                       Separation 36.20        63.84  101.52                                         ______________________________________                                        d 2        1.00         1.17   1.85                                           d 4        8.26         8.09   7.41                                           d 8        16.62        7.10   2.53                                           ______________________________________                                                 r 3 is aspherical.                                                            A = 0                                                                         B = -4.19556 × 10.sup.-5                                                C = -2.69123 × 10.sup.-7                                                D = -1.14486 × 10.sup.-9                                                E = -1.06748 × 10.sup.-11                                               r 7 is aspherical.                                                            A = 0                                                                         B = 1.21244 × 10.sup.-5                                                 C = 3.43521 × 10.sup.-8                                                 D = 0, E = 0                                                                  r 10 is aspherical.                                                           A = 0                                                                         B = -3.33544 × 10.sup.-5                                                C = -5.37753 ×  10.sup.-8                                               D = -4.17385 × 10.sup.-10                                               E = -6.26109 × 10.sup.-13                                      ______________________________________                                    

                  TABLE 1                                                         ______________________________________                                                example 1 example 2 example 3                                         ______________________________________                                        D.sub.3w -D.sub.3t                                                                      14.14       14.20     14.09                                         3(D.sub.2w -D.sub.2t)                                                                   2.80        2.34      2.55                                          3(D.sub.1t -D.sub.1w)                                                                   2.80        2.34      2.55                                          F.sub.1 /F.sub.3                                                                        -39.29      -39.63    -39.54                                        F.sub.2 /F.sub.3                                                                        -5.99       -5.59     -5.85                                         F.sub.3 /F.sub.w                                                                        0.70        0.70      0.70                                          F.sub.4 /F.sub.w                                                                        -0.76       -0.76     -0.75                                         ______________________________________                                    

There are next shown numerical examples in which the third lens unit isconstructed with a positive single lens having a strong convex surfacefacing the image side.

    ______________________________________                                        Numerical Example 4 (FIGS. 7, 10(A), 10(B) and 10(C))                         ______________________________________                                        F = 36.2-101.5   FNo = 1:4.6-8.8   2ω = 61.8°-24.0°       r 1 = 19.418                                                                            d 1 = 1.50  n 1 = 1.77250                                                                             ν 1 = 49.6                               r 2 = 16.180                                                                            d 2 = Variable                                                      r 3 = 30.730                                                                            d 3 = 1.50  n 2 = 1.83400                                                                             ν 2 = 37.2                               r 4 = 18.698                                                                            d 4 = Variable                                                      r 5 = 23.309                                                                            d 5 = 5.00  n 3 = 1.49700                                                                             ν 3 = 81.6                               r 6 = -14.879                                                                           d 6 = 1.00                                                          r 7 = Stop                                                                              d 7 = Variable                                                      r 8 = -57.616                                                                           d 8 = 3.20  n 4 = 1.60342                                                                             ν 4 = 38.0                               r 9 = -24.757                                                                           d 9 = 4.68                                                          r 10 = -12.817                                                                          d 10 = 1.70 n 5 = 1.69680                                                                             ν 5 = 55.5                               r 11 = -455.372                                                               ______________________________________                                        Variable   Focal Length                                                       Separation 36.20        64.34  101.51                                         ______________________________________                                        d 2        8.53         8.66   8.49                                           d 4        1.72         1.59   1.75                                           d 7        16.77        6.93   2.11                                           ______________________________________                                                 r 1 is aspherical.                                                            A = 0                                                                         B = -3.48999 × 10.sup.-5                                                C = -2.31998 × 10.sup.-7                                                D = -9.41482 × 10.sup.-10                                               E = -5.02295 × 10.sup.-12                                      ______________________________________                                    

    ______________________________________                                        Numerical Example 5 (FIGS. 8, 11(A), 11(B) and 11(C))                         ______________________________________                                        F = 36.2-101.5   FNo = 1:4.6-8.8   2ω = 61.8°-24.0°       r 1 = 18.582                                                                            d 1 = 1.50  n 1 = 1.77250                                                                             ν 1 = 49.6                               r 2 = 15.811                                                                            d 2 = Variable                                                      r 3 = 33.582                                                                            d 3 = 1.50  n 2 = 1.80610                                                                             ν 2 = 41.0                               r 4 = 18.105                                                                            d 4 = Variable                                                      r 5 = 21.679                                                                            d 5 = 5.00  n 3 = 1.49700                                                                             ν 3 = 81.6                               r 6 = -14.535                                                                           d 6 = 1.00                                                          r 7 = Stop                                                                              d 7 = Variable                                                      r 8 = -63.081                                                                           d 8 = 3.20  n 4 = 1.58144                                                                             ν 4 = 40.8                               r 9 = -25.420                                                                           d 9 = 4.68                                                          r 10 = -12.950                                                                          d 10 = 1.70 n 5 = 1.69680                                                                             ν 5 = 55.5                               r 11 = -985.684                                                               ______________________________________                                        Variable   Focal Length                                                       Separation 36.20        64.25  101.50                                         ______________________________________                                        d 2        10.23        10.10  9.92                                           d 4        1.42         1.56   1.73                                           d 7        16.66        6.79   2.06                                           ______________________________________                                                 r 1 is aspherical.                                                            A = 0                                                                         B = -2.54915 × 10.sup.-5                                                C = -2.37724 × 10.sup.-7                                                D = 3.0728 × 10.sup.-10                                                 E = -1.06680 × 10.sup.-11                                               r 3 is aspherical.                                                            A = 0                                                                         B = -1.65774 × 10.sup.-5                                                C = -1.38823 × 10.sup.-7                                                D = 0, E = 0                                                                  r 9 is aspherical.                                                            A = 0                                                                         B = -2.58518 × 10.sup.-5                                                C = -1.72514 × 10.sup.-7                                                D = 6.63195 × 10.sup.-10                                                E = -7.02040 ×  10.sup.-12                                     ______________________________________                                    

    ______________________________________                                        Numerical Example 6 (FIGS. 9, 12(A), 12(B) and 12(C))                         ______________________________________                                        F = 36.2-101.5   FNo = 1:4.1-8.8   2ω = 61.8°-24.0°       r 1 = 50.000                                                                            d 1 = 1.50  n 1 = 1.80518                                                                             ν 1 = 25.4                               r 2 = 46.447                                                                            d 2 = Variable                                                      r 3 = 28.468                                                                            d 3 = 1.50  n 2 = 1.85026                                                                             ν 2 = 32.3                               r 4 = 21.758                                                                            d 4 = Variable                                                      r 5 = 60.136                                                                            d 5 = 6.00  n 3 = 1.43387                                                                             ν 3 = 95.1                               r 6 = -13.197                                                                           d 6 = 1.00                                                          r 7 = Stop                                                                              d 7 = Variable                                                      r 8 = -166.800                                                                          d 8 = 3.50  n 4 = 1.54814                                                                             ν 4 = 45.8                               r 9 = -31.753                                                                           d 9 = 4.83                                                          r 10 = -14.455                                                                          d 10 = 1.70 n 5 = 1.69680                                                                             ν 5 = 55.5                               r 11 = 147.439                                                                ______________________________________                                        Variable   Focal Length                                                       Separation 36.20        64.26  101.55                                         ______________________________________                                        d 2        1.00         0.93   1.56                                           d 4        8.86         8.93   8.30                                           d 7        17.11        6.86   2.12                                           ______________________________________                                                 r 3 is aspherical.                                                            A = 0                                                                         B = -4.15008 × 10.sup.-5                                                C = -2.15803 × 10.sup.-7                                                D = -1.37123 × 10.sup.-9                                                E = -5.32786 × 10.sup.-12                                               r 6 is aspherical.                                                            A = 0                                                                         B = 3.22540 × 10.sup.-5                                                 C = 1.10695 × 10.sup.-7                                                 D = 0, E = 0                                                                  r 9 is aspherical.                                                            A = 0                                                                         B = -3.64976 × 10.sup.-5                                                C = -5.06977 × 10.sup.-8                                                D = -5.04985 × 10.sup.-10                                               E = - 1.03634 × 10.sup.-12                                     ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                                example 4 example 5 example 6                                         ______________________________________                                        |D.sub.3w -D.sub.3t |                                                 14.6        14.59     14.99                                         3|D.sub.2w -D.sub.2t |                                                0.33        0.95      1.69                                          3|D.sub.1t -D.sub.1w |                                                0.33        0.95      1.69                                          ______________________________________                                    

FIG. 13 and FIG. 14 are embodiments different from the above-describedones in that the signs of the refractive powers of the second and thirdlens units are inverted. The first to the third lens units each comprisea single lens. The first lens unit 1 is a negative meniscus lens convextoward the object side. The second lens unit 2 is a bi-convex lenshaving a strong convex surface facing the image side. The third lensunit is a negative meniscus lens convex toward the image side. Thefourth lens unit 4 is composed of a positive meniscus lens convex towardthe image side and a negative lens having a strong concave surfacefacing the object side. For the purpose of zooming from the wide-angleend to the telephoto end, the first to fourth lens units move toward theobject side in such a way that the separation between the first lensunit 1 and the second lens unit 2 decreases, the separation between thesecond lens unit 2 and the third lens unit 3 increases and theseparation between the third lens unit 3 and the fourth lens unit 4decreases.

For these embodiments 7 and 8, the above-described conditions (1) and(2) also apply.

    ______________________________________                                        Numerical Example 7 (FIGS. 13, 15(A), 15(B) and 15(C))                        ______________________________________                                        F = 36.15-101.98   FNo = 1:4.6-8.8   2ω = 61.8°-24.0°     r 1 = 24.178                                                                            d 1 = 1.50  n 1 = 1.69680                                                                             ν 1 = 55.5                               r 2 = 16.755                                                                            d 2 = Variable                                                      r 3 = Stop                                                                              d 3 = 1.00                                                          r 4 = 48.333                                                                            d 4 = 5.00  n 2 = 1.43387                                                                             ν 2 = 95.1                               r 5 = -12.720                                                                           d 5 = Variable                                                      r 6 = -26.023                                                                           d 6 = 1.50  n 3 = 1.85026                                                                             ν 3 = 32.3                               r 7 = -28.370                                                                           d 7 = Variable                                                      r 8 = -114.508                                                                          d 8 = 4.00  n 4 = 1.54814                                                                             ν 4 = 45.8                               r 9 = -30.116                                                                           d 9 = 4.64                                                          r 10 = -17.252                                                                          d 10 =  1.70                                                                              n 5 = 1.77250                                                                             ν 5 = 49.6                               r 11 = 142.249                                                                ______________________________________                                        Variable   Focal Length                                                       Separation 36.16        64.09  101.98                                         ______________________________________                                        d 2        10.70        10.41  9.69                                           d 5        1.50         1.78   2.50                                           d 7        17.52        6.72   0.95                                           ______________________________________                                                 r 1 is aspherical.                                                            A = 0                                                                         B = -4.1428 × 10.sup.-5                                                 C = -2.07199 × 10.sup.-7                                                D = -1.80897 × 10.sup.-9                                                r 5 is aspherical.                                                            A = 0                                                                         B = 5.11587 × 10.sup.-5                                                 C = 1.71220 × 10.sup.-7                                                 D = 0, E = 0                                                                  r 9 is aspherical.                                                            A = 0                                                                         B = -2.85035 × 10.sup.-5                                                C = 1.3479 × 10.sup.-8                                                  D = -1.88032 × 10.sup.-10                                               E = -3.14063 × 10.sup.-13                                      ______________________________________                                    

    ______________________________________                                        Numerical Example 8 (FIGS. 14, 16(A), 16(B) and 16(C))                        ______________________________________                                        F = 36.2-102.0   FNo = 1:4.6-8.8   2ω = 61.8°-24.0°       r 1 = 24.178                                                                            d 1 = 1.50  n 1 = 1.77250                                                                             ν 1 = 49.6                               r 2 = 17.280                                                                            d 2 = Variable                                                      r 3 = Stop                                                                              d 3 = 1.00                                                          r 4 = 62.072                                                                            d 4 = 5.00  n 2 = 1.49700                                                                             ν 2 = 81.6                               r 5 = -14.223                                                                           d 5 = Variable                                                      r 6 = -26.049                                                                           d 6 = 1.50  n 3 = 1.80518                                                                             ν 3 = 25.4                               r 7 = -28.375                                                                           d 7 = Variable                                                      r 8 = -112.885                                                                          d 8 = 4.00  n 4 = 1.54814                                                                             ν 4 = 45.8                               r 9 = -29.063                                                                           d 9 = 4.64                                                          r 10 = -17.130                                                                          d 10 = 1.70 n 5 = 1.77250                                                                             ν 5 = 49.6                               r 11 = 123.475                                                                ______________________________________                                        Variable   Focal Length                                                       Separation 36.19        64.02  102.00                                         ______________________________________                                        d 2        10.93        10.64  9.92                                           d 5        1.50         1.79   2.51                                           d 7        17.10        6.52   0.82                                           ______________________________________                                                 r 1 is aspherical.                                                            A = 0                                                                         B = -3.6110 × 10.sup.-5                                                 C = -1.98299 × 10.sup.-7                                                D = -1.29356 × 10.sup.-9                                                E = 0                                                                         r 5 is aspherical.                                                            A = 0                                                                         B = 3.30453 × 10.sup.-5                                                 C = 5.69713 × 10.sup.-8                                                 D = 0, E = 0                                                                  r 9 is aspherical.                                                            A = 0                                                                         B = -2.66865 × 10.sup.-5                                                C = 1.00677 × 10.sup.-7                                                 D = -1.15295 × 10.sup.-9                                                E = -4.13689 ×  10.sup.-12                                     ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                                    example 7                                                                             example 8                                                 ______________________________________                                        |D.sub.3w -D.sub.3t |                                                     16.57     16.28                                                 3|D.sub.2w -D.sub.2t |                                                    3.01      3.03                                                  3|D.sub.1t -D.sub.1w |                                                    3.01      3.03                                                  ______________________________________                                    

The above-described numerical examples have achieved a zoom ratio of 3and a good correction of aberrations as shown in FIGS. 4(A), 4(B) and4(C) through FIGS. 6(A), 6(B) and 6(C), FIGS. 10(A), 10(B) and 10(C)through FIGS. 12(A), 12(B) and 12(C), FIGS. 15(A), 15(B) and 15(C), andFIG. 16(A), 16(B) and 16(C) . Incidentally, FIGS. 4(A), 5(A), 6(A),10(A), 11(A), 12(A), 15(A) and 16(A) show the aberration curves in thewide-angle end; FIGS. 4(B), 5(B), 6(B), 10(B), 11(B), 12(B), 15(B) and16(B) in an intermediate position; FIGS. 4(C), 5(C), 6(C), 10(C), 11(C),12(C), 15(C) and 16(C) in the telephoto end. The necessary total numberof constituent lens elements is very few in view of the zoom ratio.

What is claimed is:
 1. A zoom lens comprising, in order from a longconjugate side, a first lens unit of negative refractive power, a secondlens unit of negative refractive power, a third lens unit of positiverefractive power and a fourth lens unit of negative refractive power,wherein during zooming a separation between each adjacent two of saidfirst, second, third and fourth lens units is varied.
 2. A zoom lensaccording to claim 1, wherein said first, second, third and fourth lensunits move toward the long conjugate side when zooming from a wide-angleend to a telephoto end.
 3. A zoom lens according to claim 2, whereinsaid fourth lens unit comprises, in order from the long conjugate side,a positive lens having a convex surface facing a short conjugate sideand a negative lens having a concave surface facing the long conjugateside.
 4. A zoom lens according to claim 2, wherein, when zooming fromthe wide-angle end to the telephoto end, a separation between said firstand second lens units increases, a separation between said second andthird lens units decreases, and a separation between said third andfourth lens units decreases.
 5. A zoom lens according to claim 1,satisfying the following conditions:

    |D.sub.3w -D.sub.3t |>3|D.sub.2w -D.sub.2t |

    |D.sub.3w -D.sub.3t |>3|D.sub.1t -D.sub.1w |

where D_(iw) is a separation between the i-th lens unit and the (i+1)stlens unit in a wide-angle end, and D_(it) is a separation between thei-th lens unit and the (i+1)st lens unit in a telephoto end.
 6. A zoomlens according to claim 1 satisfying the following conditions:

    -100<F.sub.1 /F.sub.3 <-10

    -9<F.sub.2 /F.sub.3 <-3

    0.5<F.sub.3 /F.sub.W <1.0

    -1.0<F.sub.4 /F.sub.W <-0.5

where F_(i) is the focal length of the i-th lens unit and F_(w) is theshortest focal length of the zoom lens.
 7. A zoom lens according toclaim 1, wherein said first lens unit and said second lens unit eachcomprise a negative single lens element.
 8. A zoom lens according toclaim 1, wherein said third lens unit comprises a cemented lens composedof positive and negative lens elements.
 9. A zoom lens according toclaim 1, wherein said first and third lens units move in unison duringzooming.
 10. A zoom lens according to claim 1, wherein at least onesurface of said first or second lens unit, at least one surface of saidthird lens unit and at least one surface of said fourth lens unit areaspherical.
 11. A zoom lens according to claim 1, wherein said first,second and third lens units each are constructed with a single lenselement.
 12. A zoom lens comprising, in order from a long conjugateside, a first lens unit of negative refractive power, a second lensunit, a third lens unit, and a fourth lens unit of negative refractivepower, said second and third lens units having refractive powers ofopposite sign to each other, wherein during zooming a separation betweeneach adjacent two of said first, second, third and fourth lens units isvaried, and wherein the following conditions are satisfied:

    |D.sub.3w -D.sub.3t |>3|D.sub.2w -D.sub.2t |

    |D.sub.3w -D.sub.3t |>3|D.sub.1t -D.sub.1w |

where D_(iw) is a separation between the i-th lens unit and the (i+1)stlens unit in a wide-angle end, and D_(it) is a separation between thei-th lens unit and the (i+1)st lens unit in a telephoto end.
 13. A zoomlens according to claim 12, satisfying the following condition:

    |D.sub.3w -D.sub.3t |>3|D.sub.1t -D.sub.1w |

where D_(iw) is a separation between the i-th lens unit and the (i+1)stlens unit in a wide-angle end, and D_(it) is a separation between thei-th lens unit and the (i+1)st lens unit in a telephoto end of the zoomlens.
 14. A zoom lens according to claim 13, satisfying the followingcondition:

    |D.sub.3w -D.sub.3t |>3|D.sub.2w -D.sub.2t |.


15. A zoom lens according to claim 12, wherein said first, second, andthird lens units each are constructed with a single lens element.